The present invention relates to an airbag device for protecting an occupant by deploying an airbag in an emergency, such as collision of a vehicle, and the like, and more particularly, to an airbag device having means for restricting a shape of an airbag when it is expanding.
As known well, an airbag device for an automobile includes an airbag and an inflator for inflating the airbag, and allows the inflator to eject gas in an emergency, such as collision of an automobile, and the like, so that the gas is supplied into the airbag and the airbag is deployed in a compartment.
There is known as this type of the airbag device an airbag device using a tear seam, a strap, an adhesive, and the like, which are broken or exfoliated with a predetermined tensile strength, as regulation means for regulating a shape of an airbag when it expands. In this airbag device, the volume of the airbag is reduced by, for example, coupling panels of the airbag coupled with each other by the regulation means at the beginning of expansion of the airbag, and when the internal pressure of the airbag reaches at least a predetermined pressure, the volume of the airbag is increased by breaking the regulation means.
An impact applied to an occupant is absorbed by breaking the tear seal and the strap or by exfoliating the adhesive.
Accordingly, it is an object of the present invention to provide an airbag device capable of easily stabilizing an impact absorbing action when an airbag deploys.
An airbag device of the present invention includes a folded airbag, an inflator for expanding the airbag, and restriction means for restricting a deployed-shape of the airbag, wherein when the inflator is actuated, the airbag is expanded until it is formed in a shape restricted by the restriction means. Then the airbag restricted by the restriction means is released or eased by an increase of the internal pressure of the airbag caused thereafter, and the airbag is largely expanded. In this respect, the restriction means is a strap, and the airbag is released or eased by tearing the strap so as to increase the length thereof.
In the airbag device of the present invention arranged as described above, the strap is composed of a base cloth formed of a belt-shaped cloth, synthetic resin or the like, which can be torn only in a lengthwise direction, and formed in a bifurcated-shape by being cut from the vicinity of an end to a mid-portion thereof along the lengthwise direction.
Two small, slender straps each having a predetermined length are formed on the one half side of the strap. Further, the other half side of the strap is arranged as a tearable portion which has a sufficient length and can be torn from a bifurcated portion of these two small straps along the lengthwise direction when the extreme ends of these small straps are pulled in a direction where they are separated from each other with a predetermined tension.
The strap restricts a deployed-shape of the airbag by coupling end sides of these small straps with confronting portions of the airbag, respectively. Further, when the internal pressure of the airbag reaches at least a predetermined pressure at a time it expands, the tearable portion is torn so as to increase the length of the strap by pulling the end sides of the respective small straps in a direction where they are separated from each other with a tension having at least a predetermined value.
In the airbag device of the present invention including the airbag, the deployed-shape of which is restricted by the strap arranged as described above, when the internal pressure of the airbag is equal to or less than the predetermined pressure at a time the airbag is expanded by actuating the inflator in an emergency, such as collision of an automobile, and the like, the airbag has a small apparent volume because the deployed-shape thereof is restricted by the strap, which causes the airbag to rapidly expand. Then, when the internal pressure of the airbag exceeds the predetermined pressure, the airbag pulls the end sides of the respective small straps of the strap with the tension having at least the predetermined value and the tearable portion is torn so as to increase the length of the strap, whereby the airbag restricted by the strap is released or eased and can be more largely expanded.
At that time, the tearable portion has the sufficient length and a load having at least a predetermined value is necessary to tear the tearable portion, and the load in turn acts as a resistance force against the expansion of the airbag (hereinafter, the resistance force is sometimes called a xe2x80x9ctear resistance forcexe2x80x9d). Therefore, even if the internal pressure of the airbag exceeds the predetermined pressure, it is prevented that restriction of the airbag is instantaneously released to suddenly expand the airbag, and that the internal pressure of the airbag is rapidly changed accordingly. Further, the internal pressure of the airbag is prevented from being excessively increased because the tearable portion is continuously torn so as to increase the length of the strap and the volume of the airbag is increased even after the internal pressure of the airbag has reached at least the predetermined pressure. As a result, the airbag device of the present invention can smoothly and sufficiently absorb an impact.